[Elecraft] K2 with rigblaster

[Jim Brown]

> I've also tried a MFJ TNC switch. Both for digital mode and microphone
> switching. When I use these devices I get interference when in mic 
> mode from
> rf pickup. With the mic alone., no problem.

In addition to Don's advice, I'll add this. Most electronic boxes have 
Pin One Problems, and that very likely includes all that you're trying 
to interconnect.  I suggest dumping the TNC switch and instead make a 
cable that goes from your Rigblaster to the K2 mic input, with shields 
connected to the CHASSIS of the K2. Build a simple 10:1 (-20dB) voltage 
divider as described in the link that Don gave you. It's often possible 
to put that inside the connectors -- it's a series R and a parallel R. I 
often put the series R in the connector for the driving box, and the 
parallel R in the mic connector.

If the bonding described in the link doesn't solve your problems, add a 
multi-turn ferrite choke to both of the cables between the K2 and the 
computer, and also to the cable connecting the Rigblaster to the 
computer.  5 turns through a typical #31 or #43 clamp-on is about right 
for 40M - 10M.

We have these problems because the guys who design ham gear and consumer 
gear and computer gear know nothing about RFI, and they ignore the 
advice of the audio engineers who discovered "The Pin One Problem" more 
than 20 years ago. The logic appears to be "audio is only 20-20,000 Hz, 
those guys can't possibly know as much about EE as we do -- our stuff 
goes to GHz!"

FWIW, I have no use for the dedicated ham interface boxes no matter 
whose name is on them -- the wiring interface for the ones I've seen are 
an invitation to RFI and hum/buzz problems, and most have Pin One 
Problems. A very good USB sound card can be bought for $70 (see the ASUS 
U5 Zonar), You can build a WinKey for about $75, or the Yankee Clipper 
SO2R box for about twice that cost.  A serial to serial cable is two 
connectors and some CAT5. Serial to USB adapters are inexpensive.

There are several tutorials on The Pin One Problem on my website.

73, Jim K9YC
Vice-Chair AES Standards Committee Working Group on EMC